Method of making transistors



man@ XR 'Tim-ch 5, i963 L ECTRQN 'BEAM SOURCE '53,980,48; mHOD OF MAKING TRANSISTORS M {lh- I l The e 3,050,431 7 Marston or* Martino TRANSISTORS 'Preston Robinson, iiiiiiznstosvn, Mess., assigner to- Sprague lectric Company, North Adams, Mass., a corporation of Massachusetts Filed Apr. i7, 1959, Ser. No. 867,247

4 Claims. .(Cl. Z50-33.3)

the method for making a transistor body.

Junction transistor devices are made up of a base'of semiconductive material on which is 'placed -clcctrodes of opposite conductivity material. transistors and other semiconductivc devices presents problems in reproducibility and accuracy.

It is an 'object of this invention to provide a semiconductor device which is made by'subjectinga body to a beam of electrodes.

It is another object of this invention to provide 'a technique for thepreparation of transistor bodies in a simple manner which accurately reproduces identical completed transistors. r

These and other objects of this invention willbecorne more apparent upon consideration of the following description taken together with the accompanying drrawing in which:

FIGURE 1 is a diagrammatic section of apparatus for making a semi-conductive device;

FIGURE 2 is a side section of a semi-conductive de vi:e created by the teehniqueof this invention with portionsof the original body removed;

FiGUllE 3 is a perspective of a transistor during preperation accordingto the tec`hn ique of this invention;

FiGURE 4 isA a perspective of the transistor of FIG- URE 3 uudera further step o'f preparation; and- FIGURE 5l is aperspective of the transistor.

This invention, in general, provides a :cans and method for producing a transistor -or a semiconduetivc ldevice through the action of a focused beam of electrons on a body to cause the body to be made into a transistor. The

ltransistor is formed 'by a 'succession of treatment steps.

Referring to FEGURE l, there is shown an'apparatus 'for treatment of a semiconductive body. The apparatus uscsan electron beam generated in any convenient'manner 'fror'n an electron beam source indicated at 10. Such a and gases or other material may be introduced into the. present invention relates to the manufacture of transistors and, more particularly, 4tothe apparatus and Rapid production of and approaches the upper surface orale bday n. 'ons places lthe opening 21 preferably close to the'body 1L The cup i9 is also provided with duct ttings 22 and 23 to provide for evacuation of the cham'oefwithi the cup 19.- In this manner, lthe control of the ambient at 'momhere in the chamber 24 and around the body 11 is effected. Gases may be evacuated from' the chamber 24 chamber 24. This provides a means for controlling the type of activity that goes on in the chamber 2d andadjacent the body 11. A second inverted cup 25 may be positioned over the estantes Mar.'5,1sc s` cup 19 and, thus, provide a second chamber 26. The. V`

cup 2S is provided with an opening 2'? for the passage of the electron beam from the source 1d. Similarly to cup 19 and its chamber 24, the cup 25 was provided with a duct 28 for introducingand removing materialnto and vided to form a third chamber 30.

All ofthe cups 19, 25 and 29 have slanted side walls at t'ne same angle as side walls 18. Thus, the cups are removable and interchangeable. Similarly, all .of the cups are provided with an opening for permitting the passage of the electron beam from thcs'ource I0. The joints between the walls of the adjacent cups are airtight as described above so thatthe apparatus can have chambers'witn various sorts of material within them through ,which the electron beam is passed. The base 17 contains a device 31 for measuring X-ray emanations. This device 3i is any satisfactory equipmentlzaving ,sensitivity to Xrrays such as a `SClNTlL- out ci the chamber 26. A third cup 2 9 mayalso be pr- '1 I face which is as closeas possible 'tothe body' 11, pref; 'A

sourceA can, for example, be of the type described in British Patent No. 714,613. It provides-a beam which is focused so` that it converges at the site of a body shown at 11 in 'FIGURE l. The body 11 is held in an encircling positioning' ring or sheettl on 'a raised mounting plat- -form 16 ina' base 1 7. As shown, the ring l-tfholds thej body 11 in the electron beam; An electrical lead 15 is attached `to the ring .14 and the lead 1S is connected into the electron beam circuit. A good electrical contact is;

' provided between the bodyll and the ring'llt. T he ring .can have its in ncr ed'gcsnged as indicated'at 12 to '.provide a Contact against the body 11 is pressed andheld inposition. The raised platform 16 bas`tapcred side walls 1S which .fo'rrn the shape of a column and -which provide an air- 'j tight joint with a correspondingly shaped skirt of a chamber-forming inverted cup. 19' placed over the side ylalls 1 18. The seal is improved by lubrication with a scaling Amaterial such las the silicontype o f joint grease .onven.

tionally used in' chemical apparatus. 'I 'he-cup .I9 may.

bemadc of glass ormctal. The upper wallof the cup 19 isfrmed with` an opening 21.l The opening 21 permits the electron beam' fromthe source 10 topass to the in a recessed form soas to lie adjacent to thelbody 11 erably directly in Contact with the body l1. On the other hand, the platform Vi6 is composed-of matcrialthat does not readily absorb X-rays. Suitable vitreous materials such as sodalime glass; thermally resistant borosilcatc" glasses, orlow alkali silica are suggested. Even the phosphate glasses are suitabie for this purpose. lt'is preferred that the metals uscd in forming the vparts of the apparatus be of a low atomic number such as aluminum, magnesium, titaniunt,'iron and so forth.. lt will be understood that suitable plastics are useful such as phenol formaldehyde 'or even h'i'gh molecular weight polyetb-yiene.

In this invention, as'emiconduetive device and, more particularly, a transistor may be f ormed by mounting a.: i

body of suitable semiconductivefmaterial in' the cup 19 and subjecting it to the action of the electron beam. The

electron beam 'may be employed to remove portions '0f 'I the semiconductive material,A to apply electrodes to the semiconductivc material, to apply leads to the semiconductive material and to otherwise transform the semiconductivematcrial into acompleted transistor. This action on the semiconductive material may all take place withfrom its posout removing the scmiconduclive material tion in the flange 12 within-the chamber 24.' The apparatus of FIGURE l is adapted to cooperate-with this treat; "ment ofthe scmiconductive material, can be evacuated by suctionpumps connected to the ducts The chamber. 24

422 and 23. Thisevacuation can serve to remove a'vapor from the chantbcrtd and'also to lower the pressure within into the chamber more effective.v l

l thechan'iber and, thus; make the electron beam projectedi ment on the 'semieonductive material.

In the operation of 'the a'pparatus'of FIGURE@ f or treatment of 'thesemiconductive material Vand the fomation of -th'e transistor, theelectron ,beam is 'swit'ched on ment is 'similar to that-'described .in my U.S. Lettcrs PstcnrNo. 2,883,544 issued April 2 1; 1959. As deseribed in the co-pending application,V the beam penetrates into the chamber 24 and. can be 'used toauack, modify and l..

adapt semiconductive material positioned tls-enchaine thcsemiconductive material.

tential of 50,000 volts, theelectron beam current of av few milligrams -will be suicient to evaporate a genna.

into an automatic operation.

The pressure maintained in the chamber 24 is controllable yand may be any desired pssure from atmospheric down to an extremely high vacuum such as 0.01 micron. Also pressures above atmosphere may be produced within thechamber 24. 1u this connection, the weight of the Upper part of the apparatus serves to permit raising of the pressure within the lower chamber. The cup 19. also may be clamped in the'side wall in order to bc held down l when containing araised pressure.

The ups 25 and 29 are employed to isolate the chasm Aber 24 i nings are maintained as small as possible so as om the ambient atmosphere around the'appara-` tus. O` enings 27 are provided through these'cups,v but these D 'to assist in the isolation of the interior of chamber 24.

from the remainder of the atmosphere through theinterf4 cession of cups and 29.

'Further gases generated within the chamber-24am re- 'I tained within the chamber and prevented from reaching theelectron beam source. Here-ngain, the aperrres 27 are kept as small as the use of th'e device will permit so that such undesirable gases are restricted in escape from the chamber 24. Further, in cases of very reactive gases,

` it' may be nessary Vto use at leastone addition'd cup,

-for example, cup 37, in order -to satisfactorily retain the -gases within the apparatus and to guard against escape..

The electron beam source is produced according to the 'conftltions'set forth in my U.S.'Letters Patent No. 2,883,544 issued April 2l, 1959.' This electron beam is introduced int'o the appara-tus througlrthe openings 27 and penetrates into the chamber 24. The 4electronbearn. can be focused and can be aimed within the chamber 24. Such focusing and aiming is shown in the aboveidentified British Patent No. 714,613.A ln this operation, the body of semi-conductive material which is to be made into a transistor or other semiconductive material is mounted in the place provided within chamber `24. 4The body isA then subjected to treatment oy the electron beam more fully described below. After the, steps of treatment, the transistor is completed and removed from the chamber 24. In order to carry out this treatment, suction pumps attached to the ducts 22 and 23- will create a reduced pressure in the chamber or remove gases produced in the chamber. The ducts 22 and 23 may be.used

to introduce gases into the 4chamber in order to achieve the desired finished transistor product.

The electron beam source is used to produce a number of phenomena within the chamber such as polymerizing a gas, applying a mask to the surface of a transistor, re-

' to give the desired results.

by direct evaporation.

vwill be'undcrstood, however, that with various types 'of i" materials, the conditions and procedures may' be var i :d

.Y The treatment of the sen-.iconductive material, accords mg to this invention, includes subjecting the semiconducwill result'in the application of a mask to the-semiconductive material.

.conductive body, the chamber can-be evacuatedv through the ducts23 or 22 so as to provide a disposal Yof the roj moved material. The electron beam is created and -fccused'by the meer.s andmethod described in my LRS.v Letters Patent 23833544 issued april 21, 1.959, ated December-.19, 1955. f f- A transistor` structure may be iceatedwith the method of this invention. by applying the e'lectroubearn against-1" 'the surface of a semiconductive body as described above.' 5 Referring to FIGURE 2.a body 43 of a semiconductive material is shown in vertical cross-section to be made up of asemiconductive material on a nickel basa-the semi.

conductivematerial isa p-type conductivity substance 'having an upper surface of an -n-type conductivity material: The body 4G is shown in solid outline with a mesa V4I. At the two sides of the mesa 4l, there is shown in dotted lines a portion of the semiconductive body 40 'rcmoved according to the process of this invention by the electron beam evaporation and the apparatus-of FIGURE,

l. The removed portions 42 of thebody 40 areI the resuit .of-the volatilization ofthe semiconductive material To efiect this evaporation, th'e body 40 is positioned inthe sheet A14 within the chamber 24, under a reduced atmosphere having a pressure low enough to lcause the electron beam to be projected againstl it without undue loss of eliiciency. Suction pumps on the outlet ducts 22'and 23 evacuate the chamber 2 4. The

moving'the mask, evaporating leads and electrodes on the semiconductor and removing the exess material from the leads and the electrodes. I is preferably operatedat a potential of at least 15,000 or 20,000 volts and possibly higher. 'An electron beam cur- The electron beam sourcerent can be produced v vhich will cause thesemiconductive' body to evaporate under the impingernent of the beam ou nium'body. This evaporation can be carried oo in such a way as to' rapidly remove portions of the body and,

thus, change its shape.. The action of the beam on the,

For example, at a po electron beam from the beam source 10 strikes the body '40 and is focused.- by previous adjustment to give the .de y

sired beamimpingemcnt. An electron beam source opcrates. at a sutiiciently' high potential so thatthe effect of its impingemcnt on the semiconductive'rnaterial of the vbody 40 results in an evaporation of the se rni' :o'riductive material by directing the beam against the portions 42.1 l These side portions are removed fr 'om-the body 40 as indi cated by the broken line sectioning. "'f'" r- After removal of the portions 42 and thecreation of a 'I A mesa41 on the bodyltt, the body '4D is subjected to the semiconductive b'ody can be determined by the measure'- ruentofthe X-ray output; The amount of removal achieved-in a given period of operation over predettamined circumstances can be established and from such' standards a specific procedure'developed 'for' creating a be used to monitor the treatment of the 'semicon ductive -body; the steps of-this proccdure can programmed Bodies of either type of vsmiconduct ive material may ibe treated in this procedure, and n-type or p-type semiconductive devices and transistors maybe provided.- It

g -desiredproducL X-ray measurement readings" can then next step of transstor manufacture. 'Referring t'o FIG- URE. 3,lthe` view 'shows the m'esa-foijmednppe'r surface 43 of the body 40. This surface '4 3 is'covered according --to this inventionwith a protective skin 44 as indicated by' Q the partial covering shown in'FI'GURE 3. The'covering 44 partly broken aw'ay inV FIGURE 3 covers the top of' the body 40-soas to protect it against subsequent depositions.l In laying down the protective'c'overing area.

is left uncovered to permittbe subsequent reception of a transistor'electrode. 'l'.'he protective c'overing 44 'is applied by deposition of 'a suitable tilm from' a-vapor in 'the chamber 24 of FlGURE-l, in 'which the bdyfl'i's positioned. The depositionis-achieved by the polymeriation of a suitable vapor such 'as pump oil, ethybsilicate,

styrene or other suitable monomer. The monomer, when heated. with -theelectron beam, polymerizes td adeposit.`

Similarly, vapors may b'e created -u'ithin the chamber 24 and deposited on the semiconductive material. In the removal "steps of burning ct protective tilms from the semiconductive materials or eva'p. l'

orating semiconductive material away from the sn face'ofthebody40.

After deposition' of the electrode 46 on the body 40,

' the other electrode.

Th'e ethylsilicate fo'rms of the coating 44 takes place in the area of the surface 43 struck by the electron-beam. This provides an accurate control of the laying dovm of the coating 44 and -permits' -The aluminum vapor then condenses when it contacts the solid silicate' 'nie deposition surface of the semiconductor and covers area 45 to fill the area witha deposit of the electrode material directly on' the semiconductive materialin an accurate pattern. It is a feature of this invention that, when depositing an electrode of an alloy metal, the evaporation by electron beam avoids any `preferential of melting of ont:4 of the' alloy elements with the result that the entire electrode metal substance is evaporated and the protective layer 44 is removed alongwith excess electrode matter overlying the protected areas of the body 46.

transferred to the sur.

The removal of the protective surface is achieved by burning ofi the covering film and'the excess electrodes material under the impingement of the electron beam.

FIGURE 4 illustrates, the next step which is a modified 'repetition' of the first step of protective coating deposition.

In 4the second 'protective Acoat deposition, the depositedcoat is applied to the surface 43 as .shown in FIGURE. 4.

. A partly-broken avv'ay coat-47 is shown applied to the surface 43 so as to cover'- the top of the body 40. In

practice,'this.coat 47 completely covers the surface43,I

except for the electrode 45 and an area 4S reserved for The coat 47 is created in the -same manneras the coat 44. As the surface 43 is completely covered, the chamber 24 is evacuated and a source of aluminum metal is evaporated bystriking it with the elec; tron beam. An aluminum vapor is created which depositing on" 'the area 484 causes a deposition of a second electrode on the mesa 41. Subsequently, a coating 47' and the excess electrode metal are removed from the mesa 41 and'the surface 43 to leave the mesa 4'1 withtwo elec'- trodes46 and 49. The electrodes 49 and 46 are then microalloyed onto n-type conductivity material of the mesa 41. .The micr'oalloyed step is carried out by focusing the electron beam on the'respective electrodes to heat the deposited electrode metal and cause it to `melt and to alloy ititothe' mesa 41. The transistor is now ready to receive the leads,-

' on surface-43 by polymerization or other suitable deposition' of a solid'iilm on the surface 43. The final protective coat 50 does not cover the electrodes 4 6'and 49u.

- which remain uncovered and exposed.

' 46 and 49 and leads 51 leading' to the electrodes. -The` rest of the conventional transistor structure is suitably- .Flnally, .leads s1 are deposited over theatso. As shown in FIGURE 5, the leads SIeXtend from their-:re-

- spective electrodes 'and are -'laid-down in lines running protected in its exposed portions by a covering of suitably@ resistant materials.' Glass or'a'tantalum are suggested as vavailable materials showing resistance to exposure to`f chlorine or other halogens excepttluorine. For protec'`" ing efec't of electron beam imping'ement, the lo'c'ally heated material upon which the beam is focused will react'l with the gas. .This reaction leads to conversion to-mprvolatile materials. Thus, the scmiconductive bodies susi' ceptibleA to this process cari be 'acted upon more quickly 'or more effectively by the use of such-gases. A pressure of l mm. of chlorine. for example, will speed up the,

removal of the semiconductive material for -a given elec-- tron beam intensity. and witheutany'appreciable etect' on the X-ray variationsproduced. In'forming transistors of silicon, this acccleration is particularly dirable as this material is more refractory than other materials in semicondu'ctive bodies. Where reactive gases such as chlorine or fluorine are used, the. apparatus mustY be -accort'iingy tion of the apparatus parts. from lluorine, known .resistant plastics such as'Balzelite or polytet-rauoroethylerle are suggested or highly resistant metals'such as nickel.' The pressure in the chamber24- may be maintained at'any desired level as described by ranging from atmospheric pressure or higher doivn'to avacutlrrl such as 0.1 micron."

The successive steps of preparation of a semiconductive device by this invention can he controlled by automatic means.

into a completed transistor hy successive'automaticI treat ments in one location with a plurality of operations. It will, thus, be seen that one of the advantages obtained by' this invention' is automation of tlansistor'manufacture. Further, the automatic operation provides [means fori v high speed treatment'with the successiv'elsteps following each other in rapid succession."v The. sensitivity ofthe control possible as a result of this'inventionenhanccs this advantage of speed, The progress of the4 treatmentof lthe semiconductive body is'followcdby the 'output ofthe- X-rayl treatment.l As the apparatus isstandardized by adaptation to bodieshavin'g` specific characteristics, the

X-ray measurement readings maybe 'charted to provide the automatic control which is necessary to automation.

'l The invention' is particularly effective iyith'bodies of 60 is-forme'd by impinging thel electrombeam on' the semifrom. the microlloyed electrodes; 46 and 49 over .the 'protective coat StlAlaterally-to theedge ofthe upper sur;

face 43. Thus; the transistor is provided with electrodes provided. Further, the 'transistor provided with a protective coatremaining on the upper surface-43'.

. As set forth'in my tto-pending application'lme'ntioned above, the volatiliza'tionfin theprocess of this invention "io- A can be 'aided so that the formationo f the transistor zdoesnot rely on volatilization alone.' The materialcan be Under' the heat.-

Another fads/aangaat 'uns lui/num is the eofip'laubn" germaniurr't.`

The X-'ray sensitivity measurement means mayjbe positioned at any point where it can effect an accurate measurement of the treatment of the. semiconductive vbody and the activity which is. taking place'on' the body surface. The platform i6 andthe sheet 14 may be ar` ranged to g'rip the semiconductve'body in 'yarious ways A to'ladapt it to the'treatment and tothe'X-ray measurei ment. Further, the carriage of the s'emiconductive body canhave mobility so as .to tum the semiconductive bodyover and* carry out the treatment on opposite faces of f y the body.

. Various adaptati sequen'tly burned ofi' under. theelectlron beam. The film conductor in the presence of the vapor. While pump oil,

ethyl silicate and styrenefmn'omer have been disclosed as providing vapors which are polymerizable to form-th desired protective' covering,`masks may be made up of other materials ha'v1ng ''the` same reaction under the im-'a pingement ofthe electron'beam on-a se nliconductive body; A

of evaporation .o'f thedepositing'metal which forms-the electrodes.' When'a'n alloy is used .to form the electrodes, 'the evaporating b'ea'm, on 'striking -the metal source, evap'.

Acrates. the entirealloy source; and, rtltt'ls,'there'is no'` selection inthe material transfers-:dond condensed'as an' electrode. These ativantagesn in aditionto the accurate Thus, the control 'Carr be made subject to auto-2 i '.A matic operation and a semiconductivebody transformednsof this invention 'may be had within the spirit thereof. For example, the mask of they" ,protective covering 44 maybe made up of a lm deposited from a suitably polymerizable vapor. which may. be subi What is claimed is: l; A process for making a scmiconductive device 'cluding the steps of projecting a' focusedbeam of eleccontrol 'referred to above, malte tb-e'inve-ntioh particularly uscful .in `the manufacturel of ,semiconductive clevices. In view of the adaptability of this inventicn to varioustypesof construction and the ruaterialsjit 'will be understood that the above-described embodiments Shangai in the' semedircction tbat'the beam of.electrons is prohave been set forth for the purpose 'of illustration andv .that it is intended that within the scope 'of the appended claims, the invention may be practiced otherwisethan as specica'lly described.' 1 -This application is a contiruatioolin-partof lrny U.S. Letters Patent N.2,333,5 44 SSu'e December 19, 1955.V

Irons against a portion of a semiconductivebody `vin the at the body surface to form a protective layer o n the cased beam of electrons against a metalcontaining body,

densing the volatilized metalic'vapor on vsaid unprotected area, and subsequently removing the'protective film and d pril.21, '1259, lsd -i.

. i l conductive bodyto project the focused beam of electrons against a different portion of tbe body, repeating the volaf tilization of the impinged portion, shifting the position of-,

' surface of thetserniconductive body, projecting-the fo- 2O volatilizing an electrode metal from said metallcontainjected, and controlling the beam projection by the meas- A ured inten'sityo the X-rays. 4. A process for making a semconductive device irairons against a portion of a semicondutivc body in the a presence of a corrosive gas, heating the impinged portion vapor-on4v theremaining -surface by saidvolatlization, measuring the intensity of the X-rays that are generated of the body and volatilizing the mpinged portion of the body to generate X-rays, shifting the' position of the semithe semiconductive body in the. focused beam, projecting I thefocused beam of electrons against a third Aportion in presente of polymerizable vapor, polymerin'ng the vapor the pr'esenceof polymerizable vapor, polymerizingthe vapor at the body surface to form a protective layer' on' the surface of 'thesemiconductive body,A providing an area of said'body surface free of said protective layerj projecting the focusedbeam of electrons against a metal containing body adjacent the surface of the semiconductive body, volatilizing an electrode metal from said metal containing body to form a metallic vapor adjacent the 'l surface of the semiconductive body, condensing the vo1a' tilized metallic vapor ou said unprotected area and sub- *sequently removing the protective film and condensed metal from the area of the body surface covered by the condensed metal 'from the area of the body surface covered by the protective layer. i- 3. A process for forming a semi-conductive body comprisingr the stepsofrprojecting a foe-used beam of elec- 35 trons against a portion of t .e body to generate X-rays and cause the portion to become heated and to be volatili/'Led away, introducing a polymerizable vapor'into the region -of the semiconductive body, polymerizing a lilm'of the protective layer by moving the b ody under the focused beam of electrons.

References Cited in the file of this patent UNITED STATES PATENTS' 2,662,957 Eisler Dec. 15, 1953 2,771,568 Steigerwald -s Nov. 20, 1956 2,778,926 Schneider ---.L Ian. 22, i957 2,860,251 Pakswcr et al. Nov. 11,1958

2,883,544 Robinson .gApr. 21, 1959 ERNEST w. `swnxatn 'I UNTED STATES PATENT .oFFiCE meut N A.3,080,2i8i

' Preston Robinson.

It is h'ereoy'fc'ertfed thateror appears in the above numbered pain-'- ent requiring correction anci-oh8 tY the -said'Letters Patent should read as conoci-ed below, l Y l A4Colunm l, line 'l`9*,' for "electrodes" read` #-1 elect.r-ons' ';f line'58, after "against insert A- which column 5, line 2.5, for electrodes" tead -felectrode column 8, line' Signed `andsea'ied`thi$ lst day of October"V` 19.63

(SEAL) Attest:

' 15Min L. LADD' Mambo.' 19635@ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,080,481 March 5, 1963 Preston Robinson It is hereby certified that error appears in the abo-ve numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l, line 19, for "electrodes" read electrons line 58, after "against" insert which column 5, line 25, for "electrodes" read electrode column 8, line 17, after "of" insert a Signed and sealed this lst day of October 1963.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

3. A PROCESS FOR FORMIMG A SEMI-CONDUCTIVE BODY COMPRISING THE STEPS OF PROJECTING A FOCUSED BEAM OF ELECTRONS AGAINST A PORTION OF THE BODY TO GENERATE X-RAYS AND CAUSE THE PORTION TO BECOME HEATED AND TO BE VOLATILIZED AWAY, INTRODUCING A POLYMERIZABLE VAPOR INTO THE REGION OF THE SEMICONDUCTIVE BODY, POLYMERIZING A FILM OF THE VAPOR ON THE REMAINING SURFACE BY SAID VOLATILIZATION, MEASURING THE INTERSITY OF THE X-RAYS THAT ARE GENERATED IN THE SAME DIRECTION THAT THE BEAM OF ELECTRONS IS PROJECTED, AND CONTROLLING THE BEAM PROJECTION BY THE MEASURED INTENSITY OF THE X-RAYS. 